1. Field of the Invention
The invention is related generally to the field of acquisition and interpretation of measurements made by well logging instruments for the purpose of determining the properties of earth formations. More specifically, the invention is related to a method for correction of dielectric effects using multifrequency resistivity data.
2. Background of the Art
Electromagnetic induction and wave propagation logging tools are commonly used for determination of electrical properties of formations surrounding a borehole. These logging tools give measurements of apparent resistivity (or conductivity) of the formation that when properly interpreted are diagnostic of the petrophysical properties of the formation and the fluids therein.
The physical principles of electromagnetic induction resistivity well logging are described, for example, in, H. G. Doll, Introduction to Induction Logging and Application to Logging of Wells Drilled with Oil Based Mud, Journal of Petroleum Technology, vol. 1, p. 148, Society of Petroleum Engineers, Richardson Tex. (1949). Many improvements and modifications to electromagnetic induction resistivity instruments have been devised since publication of the Doll reference, supra. Examples of such modifications and improvements can be found, for example, in U.S. Pat. No. 4,837,517; U.S. Pat. No. 5,157,605 issued to Chandler et al, and U.S. Pat. No. 5,452,761 issued to Beard et al.
It has long been known that resistivity measurements made by a logging tool are responsive not only to formation resistivity (or conductivity), but also to the dielectric properties of the formation. See, for example, U.S. Pat. No. 5,187,661 to Sinclair, U.S. Pat. No. 5,367,262 to Manning, U.S. Pat. No. 5,345,179 to Habashy et al., U.S. Pat. No. 5,811,873 two Meyer Jr., U.S. Pat. No. 6,092,024 to Wu, and U.S. Pat. No. 6,892,137 to Hoaglund.
Some of the prior art methods address the problem of resistivity determination using model-based relations between the resistivity and a dielectric constant. The present invention addresses the problem of resistivity determination without using such models.